On June 19, 2009, an Eurocopter France EC 120B was involved in an aviation accident near Mannheim, DE. No fatalities were reported. This summary draws on records from the German Federal Bureau of Aircraft Accident Investigation (BFU).
On 19 June 2009, an EC 120B crashed into a cornfield near Mannheim-City during a training autorotation. Three people were lightly injured and the helicopter was heavily damaged.
Overview and flight details On 19 June 2009, a Eurocopter France EC 120B helicopter was involved in an accident near Mannheim, Germany. The aircraft was operating a training flight from Koblenz to Mannheim-City. The crew consisted of a flight instructor and two students. The purpose of the final part of the flight was to perform a practice autorotation from an approach with a 180-degree left turn. ## Sequence of events According to the crew, the student in the right front seat initiated the autorotation south of the airfield, abeam runway 27, at approximately 2,000 ft AMSL. After the descent was stabilized, the instructor set the twistgrip on the collective control to “Idle.” After the left turn toward the airfield, the student determined at about 600 ft AMSL that the altitude was too low and the airfield could no longer be reached, and announced a go-around. The instructor then returned the twistgrip to “Flight” so the engine could resume driving the main rotor. The crew heard a rotor overspeed warning and pulled the collective to bring the rotor speed back into the normal range. Immediately afterward, an underspeed condition occurred, and the crew noticed that the engine was not producing the expected power. The instructor took control and, at about 200 ft AGL, made a sharp left turn of about 100 degrees, initiated a flare, and arrested the helicopter. He reported a bang and a severe vibration just before touchdown when pulling the collective. The helicopter touched down hard at 12:11 local time in a cornfield in front of runway 27, with no forward speed. The skids broke off from the rear cross tube. The main rotor struck through the tail boom. The emergency locator transmitter activated, with its signal first recorded at 12:11:33. The crew exited the helicopter through the left door and sustained minor injuries. ## Aircraft and maintenance The EC 120B is a light multirole helicopter for up to five occupants, equipped with a three-blade main rotor, a Fenestron tail rotor, and skid landing gear. The accident aircraft was built in 2002, had serial number 1320, and was powered by a Turbomeca Arrius 2F turbine engine. Its maximum takeoff mass was 1,715 kg, and its current mass was about 1,427 kg. The last maintenance check was performed on 12 June 2009 at 1,023 operating hours; total operating time was 1,048 hours. The report notes that during student training, the same helicopter had previously experienced several unintended engine shutdowns, including during autorotations from hover and once during a tail rotor control failure exercise. ## Findings at the accident site The accident site was about 250 m east of asphalt runway 27 at Mannheim-City, in a cornfield at about 309 ft AMSL. The helicopter came to rest on its fuselage floor facing 170 degrees. The skids had broken off the rear cross tube and pointed upward; the cross tubes were twisted rearward. The tail boom was separated ahead of the Fenestron vertical fin. The three main rotor blades showed varying damage, with one blade detached and lying near the wreckage. Fragments of the tail boom, Fenestron drive shaft, and Fenestron were found up to 44 m east of the wreckage. The twistgrip on the collective was in the “Flight” position. The helicopter carried 124 kg of fuel, with no fuel leak at the site. Fuel filters were full and clean. Main gearbox oil level was within limits; Fenestron gearbox oil level could not be determined, though lubricant traces were found outside the gearbox housing and on the ground. After recovery, the engine and control settings were inspected by an engine manufacturer representative, with no irregularities found. ## Investigation and testing The BFU investigated the accident. A replay flight was conducted with a helicopter of the same type, involving BFU personnel, to assess main rotor speed behavior during autorotation with turns and to determine whether power recovery at the end of an autorotation differed from other helicopters of similar size. One autorotation was also performed with the engine shut down to determine whether an audible difference could be perceived between a shut-down engine and an idling engine. The three participating pilots described the autorotation characteristics as comparable to other types, but noted that applying engine power at the end of the autorotation required careful coordination between opening the twistgrip and pulling the collective to avoid main rotor overspeed. With practice, power recovery appeared manageable. No audible difference was perceived between a shut-down engine and an idling engine during autorotation. The right collective control, which housed the twistgrip stop mechanism, was removed from the wreckage and examined with support from Federal Police technicians, Eurocopter Deutschland, and later at Eurocopter France’s facility. No technical reasons or deviations from technical documentation were found that could explain why the twistgrip could be closed past the electrical lock in a de-energized state. The entire mechanism, stop-pin adjustment, and spring force for the pin met specifications. After removing three lock washers totaling 0.3 mm to adjust the stop pin, the twistgrip could no longer be closed. Eurocopter France stated that comparable incidents in which a twistgrip could be closed while de-energized were not known to them.